When the water in the skin was used up, she placed the child under one of the shrubs. Bible see other translations

“placed.” For contextual reasons, the verb should be understood as “placed” or “left,” not “threw,” or “cast.”a Ishmael was now at least 16 and may have been as old as 19 (Ishmael was born when Abraham was 86; Gen. 16:16), but it expresses Hagar’s desperate action to keep her son in the shade and alive a little longer. It is likely that Ishmael was weak and dehydrated and had grown faint, and Hagar was distressed and did not know what else to do, thus her action is somewhat hopeless desperation. She put him in the shade under a bush and walked a distance away to separate herself from her son. Indeed, it is likely that they both would have died without divine help at that time.

There is likely an intentional parallel between Abraham with Ishmael and then Abraham with Isaac (Gen. 22). In both cases, the child is on a journey to an unknown place; then the child is on the edge of death; then an angel of God intervenes, calling out from heaven; then the parent sees a way out (for Hagar, the water; for Abraham, the ram in the thicket); and then there is a promise of future blessing.b

“she placed the child under one of the shrubs.” It seems Ishmael was too weak to go on. The rabbis suggest that he was sick.

Victor Hamilton, The Book of Genesis: Chapters 18-50 [NICOT], 76, 83.
Everett Fox, The Five Books of Moses, 88.

Commentary for: Genesis 21:15